Fluid overload and chronic hypertension are the most common indications for diuretics. The diuretic response varies between different types and depends on underlying renal function. In patients with congestive heart failure, diuretics appear to reduce the risk of death and worsening heart failure compared with placebo, but their use in acute decompensated heart failure is questionable. Diuretics are also widely used in chronic kidney disease to prevent or control fluid overload, and treat hypertension. In acute kidney injury, there is no evidence that they improve renal function, speed up recovery, or change mortality. In patients with chronic liver disease and large volume ascites, paracentesis is more effective and associated with fewer adverse events than diuretic therapy, but maintenance treatment with diuretics is indicated to prevent recurrence of ascites. Mannitol has a role in liver patients with cerebral oedema and normal renal function. The use of diuretics in rhabdomyolysis is controversial and restricted to patients who are not fluid deplete. In conditions associated with resistant oedema (chronic kidney disease, congestive heart failure, chronic liver disease), combinations of diuretics with different modes of action may be necessary. Diuresis is easier to achieve with a continuous furosemide infusion compared with intermittent boluses, but there is no evidence of better outcomes. The role of combination therapy with albumin in patients with fluid overload and severe hypoalbuminaemia is uncertain with conflicting data.